Salmon Creek Restoration and Water Supply Planning

Client: Okanogan Irrigation District

Location: Okanogan, WA

Summary: Listing of endangered salmonids in the Columbia River system prompted concern by the Colville Confederated Tribes (CCT) for their recovery, and on the part of irrigated agriculture as to potential effects on their water supply. A proactive partnership between the Tribes and the Okanogan Irrigation District (OID) was formed to explore opportunities that could both protect irrigation service and restore flows to a reach of Salmon Creek dewatered by irrigation diversions for more than 80 years. Our objective was to provide passage for salmon to more than eleven miles of high quality habitat above the diversion dam.

In a series of assignments, Cardno ENTRIX (1) developed a range of feasible alternatives and water supply plan to restore instream flows and anadromous salmonids to Salmon Creek; (2) prepared a concept design for rehabilitation of Salmon Creek; and (3) prepared an EIS addressing the proposed rehabilitation of Salmon Creek, as part of the Bonneville Power Administration?s (BPA) mid-Columbia Basin salmon mitigation strategy.

Key benefits of the project include:

• Restore passage for federally listed steelhead and spring Chinook salmon through a 4.3 mile degraded river reach that has been dewatered for 80 years.
• Restore access to 11 miles of high quality habitat above the irrigation diversion dam.
• Improve local irrigation infrastructure, limit exposure to liabilities, and continue reliable irrigation water supply to a small rural economy that depends upon its agricultural base.

The feasibility assessment and water supply plan evaluated water supply alternatives capable of meeting the needs of both irrigation and instream flows. Cardno ENTRIX facilitated a Joint Committee of the Tribes and District through the planning process, leading a series of workshops to examine the alternatives, achieve a systems understanding of the instream needs and irrigation water requirements as a functional whole, and review the fisheries biology and stream geomorphology. A key outcome was the Committee?s agreement on a water supply program that paved the way to fund and initiate stream rehabilitation for salmon recovery. In all, some 28 water supply alternatives were identified and analyzed. By a combination of improved existing irrigation infrastructure, water storage, water conservation, and strategic water exchanges and water right transfers, Cardno ENTRIX helped design an overall workable solution in a small watershed with very limited firm water supply. The plan achieved its goal of developing recommendations that can provide both reliable irrigation water supply and passage flows for summer steelhead and spring chinook, allowing access to 11 miles of high quality habitat above the district?s diversion dam. An integrated water system operations and hydrology model was developed to evaluate alternatives in terms of fish flow requirements.

The rehabilitation concept addressed site-specific treatment of eroding stream banks, revegetation and land use management measures to improve local channel and habitat conditions that would allow the currently dewatered stream to return to a natural, stable, and free-flowing state. Extensive reconstruction of the lower two miles of creek above the confluence with the Okanogan River was recommended.

The EIS considered both stream rehabilitation and alternative means to supply irrigation water to the Okanogan Irrigation District. It used the water supply alternatives analysis and stream rehabilitation concept design to build NEPA alternatives for evaluation. The Washington Department of Ecology used the EIS to achieve SEPA compliance as well. Issues included instream flows, landowner acceptance, socioeconomic impacts, ESA, cultural resources, and water policy/impacts.